Hydraulic anti-shock device



DC. 28, 1965 -r HYDRAULIC ANTI-SHOCK DEVICE 5 Sheets-Sheet 1 Filed Feb.5, 1965 Emma Dec. 28, 1965 J. PlRET 3,225,541

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Dec. 28, 1965 J, PlRET 3,225,541

HYDRAULIC ANTI-SHOCK DEVICE Filed Feb. 5, 1965 5 Sheets-Sheet 5 D66. 28,1965 J, Pl

HYDRAULIC ANTI-SHOCK DEVICE 5 Sheets-Sheet 4.

Filed Feb. 5, 1965 Dec. 28, 1965 J. PIRET 3,225,541

HYDRAULIC ANTI-SHOCK DEVICE Filed Feb. 5, 1965 s Sheets-Sheet 5 6[ZEN/M) 9 1M5 4 United States Patent HYDRAULIC ANTI-SHOCK DEVICE JeanPiret, Vernouillet, France, assignor to Societe Anonyme SimcaAutomobiles, Paris, France Filed Feb. 3, 1965, Ser. No. 430,156 Claimspriority, application France, Feb. 5, 1964, 962,670 Claims. (Cl. 60-52)The present invention relates to a hydraulic anti-shock device forcontrolling a double-acting jack piston by means of a hydraulic fluidcontinually furnished by a pump, and particularly to devices of thistype in which the hydraulic jack is actuated by a fluid to controlmachinetools.

In order to achieve the alternating displacement of a mechanical organsuch as a tool holder, a pressure plate, or a mechanical shovel, it isknown to use a hydraulic circuit which acts alternately on thedouble-acting piston of a jack, which piston is rigidly connected to theunit to be displaced.

To this end, each face of the control piston is connected, selectivelyand alternatively, on the one hand, to the delivery circuit underpressure and, on the other hand, to the hydraulic inlet circuit of thesame pump.

The distributor comprises, in general, a principal element in the formof a slide valve carrying a piston which, when it assumes anintermediate, or central, position between its two extreme positions,connects the delivery circuit to the inlet circuit of the pump. Thecontrol of this slide valve is etfectuated most often by twoelectromagnets each mounted to push a respective end of the slide valve.Between the pump and the distributor is disposed in parallel a pressureregulator which determines the maximum pressure of the control fluidapplied to the control piston and contained in the control jack.

In order to start the control piston in one direction, one of thewindings of the electro-magnets is excited, which has the effect ofprovoking the displacement of the slide valve and the placing incommunication of one of the faces of the control piston with thedelivery circuit and of the other face of the piston with the circuitfor returning hydraulic fluid to the pump inlet vat. After the movementof the slide valve in the distributor, and prior to the response of theregulator designed to short-circuit a portion of the delivery pressure,a hydraulic starting or compression shock wave appears in hydrauliccircuits such as those associated with machine-tools, which waveparticularly depends on the dimensions of the jack and of the masses tobe placed in movement, and on the value of the operative pressuredetermined by the pressure regulator.

When the control piston has arrived at the end of its travel path, andwhen the slide valve is returned to its central position by thede-energization of the previously excited electro-magnet, the chamberwhich has previously been expanded by the delivery pressure abruptlyliberates a large potential energy due to the fact that it is placed incommunication with the circuit for returning fluid to the valve, theliberation of this potential energy creating a decompression shock wave.

Moreover, this decompression shock wave is reinforced by the placingunder pressure of the opposed face of the control piston in the casewhere the Winding of the second electro-magnet is energized when thefirst electro-magnet is de-energized.

It may be readily appreciated that the shock waves which are produced ateach starting or reversal of the movement of the control piston duringthe transient periods in the hydraulic circuit create serious drawbackssince they necessarily create leaks in the delivery circuit PatentedDec. 28, 1965 in the vicinity of connections and joints and, moreover,cause the premature deterioration of the hydromechanical transmissionsas a result of the repeated and large strain produced by the elevatedpressure points. To these inconveniences are added the considerable lossof hydraulic fluid due to the above-mentioned leaks and the replacementcost of prematurely deteriorated pieces, as well as the labour costsnecessary for the replacement of these pieces.

The present invention is intended to be applied to a hydraulic jackwithin which there is found a double-acting control piston furnishedwith a straight, or partially straight shank, this jack being connected,on the one hand to a hydraulic fluid delivery circuit adapted to beplaced in communication alternatively with one or the other surface ofthe control piston through the intermediary of a principal distributorfurnished with a double-piston slide valve controlled alternatively bytwo electro-magnets, and on the other hand, a circuit for returning thehydraulic fluid to an inlet vat, which circuit communicatesalternatively either with one or the other of the control-piston facesor simultaneously with the two faces of said piston and the deliverycircuit of the pump through the intermediary of said principaldistributor.

Devices are already known which function to damp the pressure shocks onthe control piston by diminishing the acceleration of the hydraulicfluid in the delivery circuit. However, these devices do not prevent thecreation of pressure shocks and although these shocks are no longerapplied to the jack piston, the reactions of these shocks continue toact on the pump and on at least some of the joints of the deliverycircuit.

A known hydraulic anti-shock device comprises, in the delivery circuit,between the delivery pump and the principal distributor, a pressureregulator capable of connecting the delivery circuit to the returncircuit to the vat for two different pressure values, referred to as themaximum operative pressure and the minimum operative pressure,respectively. The pressure regulator comprises a valve interposedbetween the delivery circuit and the vat-return circuit and rigidlyconnected to a piston defining two chambers, one of which is situatedbelow the piston and communicates directly with the return circuit andthe other of which chambers is situated above the piston andcommunicates with the delivery circuit through the intermediary of acalibrated channel. The upper chamber is furnished with a restrainingspring which urges the valve into its closing position and is adapted tobe connected to the vat-return circuit through the intermediary of amaster distributor controlled by means of an electromagnet.

In the case of a hydraulic anti-shock device associated with a hydraulicmotor, it could be conceived to control the electro-magnets of theprincipal distributor and of the master distributor by means of anelectronic timedelay circuit which could theoretically give acceptableresults in so far as concerns the elimination of the formation of shockwaves even for the case of extremely short work cycles. Such a devicewould neverthless present the drawback of not controlling the placingunder minimum pressure of the delivery circuit by the master distributorand by the principal distributor. As a result the possibility of shockWaves which would be harmful to the apparatus would not be completelyeliminated.

At the time of the stopping of the rotating motor prior to the reversalof the direction of rotation of said motor, the shock waves areestablished in a relatively slow manner, with the result that theresponse of the pressure regulator could intervene with a delay of oneor two seconds with respect to the instant when this latter is commanded(anticipated command).

One could then control the displacement of the principal distributor inorder to prepare the reversal of direction of rotation of the rotatinghydraulic motor and then progressively reestablish the maximum operativepressure in the delivery circuit, by means of a pressure regulator,through the master distributor one to two seconds after having commandedthe principal distributor. In order to definitively eliminate theformation of shock waves, the time-delay of the control of thedistributors should be at least slightly greater than the response timeof the pressure regulation of the device. It is known that the responsetime of the distributor depends in a large part on the temperature ofthe hydraulic fluid, on its viscosity, on the energization voltage ofthe electromagnets, on the friction of the various movable elements ofthe distributors, etc., so that the electronic time delay, for reasonsof security, should be adjusted in accordance with the maximum responsetimes of the distributors, if one desires to eliminate the formation ofshock waves in all cases. The result thereof would be a considerableloss of time, particularly when it would be desired to apply theelectronically controlled, hydraulic, anti-shock device to a hydraulicjack whose work cycle should be of the order of one to three seconds.

It has been noted that generally in a hydraulic jack the shock wave isestablished in /100 of a second. It would thus be desirable to provide atime interval of the order of of a second between the control of the twodistributors in order to eliminate, with a margin of security, thepossible shock waves, which would not increase in an excessive fashionthe duration of a work cycle, even when this latter is of the order of lto 3 seconds. Similarly, in the decompression phase, the control of theprincipal distributor could intervene as soon after the response of thepressure regulator, i.e. when the delivery pressure is a minimum. Forthe above-noted reasons, it is not desirable to construct such ahydraulic anti-shock device using electronic means for the anticipatedcontrol of the master distributor controlling the pressure regulator andfor the delayed control of the principal distributor. Moreover theelectronic units are expensive and require highly skilled maintenancepersonnel.

It is an object of the present invention to eliminate all of theabove-noted inconveniences and notably to provide a hydraulic anti-shockdevice for the control of the jack piston, which device, duringstarting, stopping and the reversal of the direction of motion of thejack piston at any point in its travel path, prevents the formation ofpressure shocks and permits short work cycles for the jack whileassuring the delivery of hydraulic fluid which is subjected to nopressure against one of the faces of said jack piston, the obtaining ofa small operative pressure during a time period extending between theenergization or deenergization of one or more electro-magnets and theresponse of the pressure regulator, as well as a progressive increase inthe fluid pressure until reaching a maximum operative pressure and aprogressive decrease of the pressure until attaining the minimumoperative pressure during the reverse process.

The hydraulic anti-shock device associated with a hydraulic jackfurnished with a piston whose two faces, through the intermediary of aprincipal distributor commanded alternately by two electro-magnets, arecapable of being connected either alternately with the delivery circuitor the return circuit of a pump, or simultaneously with the twocircuits, comprises: in the delivery circuit downstream of the principaldistributor, a pressure regulator furnished with a valve interposedbetween the delivery circuit and the return circuit to the inlet vat,and rigidly connected to a piston defining two chambers, the lowerchamber of which communicates directly with the delivery circuit and theupper chamber of which, furnished with a restraining spring urging thevalve into its closing position, communicates through the intermediaryof a calibrated channel with the delivery circuit; a master distributorconnected, on the one hand to the upper cham ber of the valve pistonand, on the other hand, to the vatreturn circuit, and capable of beingcontrolled by an electro-magnet in such a manner as to destroy orestablish the communication between the upper chamber of said valvepiston and the vat-return circuit; and an electric circuit furnishedwith switches and relays for starting up and stopping the pump motor andfor controlling the various electro-magnets, this hydraulic anti-shockdevice being characterized in that it comprises end-of-travel switchescapable of being actuated by cams arranged in such a manner as to beable to follow the displacement of the armature of the correspondingelectro-magnets of the distributors, the end-of-travel switch of themaster distributor being disposed in the electric circuit of theelectro-magnets of the principal distributor in such a way that itcannot be closed by its corresponding cam and does not permit theexcitation of one of the electro-magnets of the principal distributoruntil the master distributor is in its neutral position, while theend-of-travel switches of the principal distributor are disposed in thecircuit of the electro-magnet of the master distributor in such a waythat neither can be closed by its corresponding cam and does not permitthe excitation of the electro-magnet of the master distributor until theprincipal distributor occupies one of its two extreme positions.

These and other objects, features and advantages of the presentinvention will become more readily understood from the followingdescription of various embodiments of the present invention, given onlyby way of non-limiting example, together with the attached drawings, inwhich:

FIG. 1 shows a hydraulic circuit of a jack, e.g. for a machine-tool,this jack being furnished with a hydraulic anti-shock device capable ofbeing controlled according to the present invention;

FIG. 2 shows a hydraulic circuit of a jack, e.g. for a machine-tool,this jack being furnished with a second type of hydraulic anti-shockdevice capable. of being controlled according to the present invention;

FIG. 3 is a schematic diagram of a first embodiment of an electriccontrol and monitoring circuit according to the present invention forthe motor, pump and electromagnets of the distributors of the device ofFIG. 1;

FIG. 4 shows a schematic diagram of a second embodiment of the controland monitoring circuit of the present invention; and

FIG. 5 is a schematic diagram of a third embodiment of the control andmonitoring circuit of the present invention.

Turning first to FIG. 1, there is shown a jack 1, for a machine-toole.g., comprising a double-acting piston 2 to which is rigidly connecteda shank 3 furnished with a tool, not shown. The piston 2 defines twochambers 4 and 5 in the jack 1, each of these chambers communicating,through the intermediary of a respective one of conduits 6 and 7, with arespective one of the end chambers 8 and 9 situated to either side of acentral chamber 10 ofa principal distributor 11. Through theintermediary of a double piston slide valve 12, each of the end chambers8 and 9 communicates with the central chamber 10 and, through theintermediary of said central chamber, with the delivery circuit 13 of apump P driven by a motor M, these end chambers 8 and 9 also beingconnected to the return circuit 14 of the inlet vat 15 of pump P. In thedescription to follow, it should be understood that the term returncircuit is intended to include all of the conduits leading to the vat 15of pump P. When the double piston slide valve 12 is in its intermediateposition, as shown in FIGS. 1 and 2, each of the chambers 4 and 5 ofjack 1 communicates with the delivery circuit 13 as well as with thereturn circuit 14 leading to the inlet vat 15 of pump P.

.37. of electro-magnet EA to the shank 41 in order to diminish the speedof disregulator 16, comprising a piston 17 whose lower surface isrigidly connected to a valve 18 controlling an opening 19 through theintermediary of which the delivery circuit 13 communicates directly withthe circuit 14 for returning fluid to the inlet vat 15 of pump P. On itsupper surface, the regulator piston 17 carries a hollow cylinder 20adapted to slide in an inpermeable manner in a cylindrical space 21 ofthe regulator. In this space 21 is housed a restraining spring 22 whichurges the piston 17 downwardly in order to close the opening 19 by meansof the valve 18, which valve comprises a central orifice 23 connectingsaid space 21 with the circuit 14 for returning fluid to the inlet vat15. The piston 17 also comprises an eccentric calibrated channel 24which creates a communication between a chamber 25, connected to thedelivery circuit 13 and situated below the lower face of piston 17, anda chamber 25a, delimited by the upper surface 17, the housing ofregulator 16, and the outer periphery of hollow cylinder 20. Thisannular chamber 25a is connected to the cylindrical space 21 through theintermediary of a calibrated channel 26, a retaining valve 27 urged by aregulatable spring 28 in a direction opposed to the flow of deliveryfluid, a chamber 29 in which are housed said valve 27 and theregulatable spring 28, and a channel 26a. The calibrated channel 26 isalso connected to a first connecting conduit 13, referred to as themaster conduit, creating a communication between the delivery side ofpump P and a first master distributor 30. This distributor 30 alsocomprises a pair of chambers 31 and 32, each of which is disposed at arespective end of distributor 30, continually communicating with thereturn circuit 14 of the inlet vat 15 of the pump P. Distributor 30 alsocomprises a central chamber 33 into which empties the first masterconduit 13. The first master distributor 30 further comprises a doublepiston slide valve 34 which, in its intermediate position, prevents anycommunication between the master conduit 13' and the end chambers 31 and32, and thus between conduit 13' and the return circuit 14.

At each of its ends, the principal slide valve 12 is urged by therestraining springs 35 and 36 towards its intermediate position, thisslide valve co-operating with the armatures 37 and 33 of electro-magnetsEA and EA respectively, each of which controls the displacement of saidslide valve towards a respective end of distributor 11.

Armature 37 serves as an abutment for a control shank 41 which is guidedin support bearing 44 and urged towards said armature 37 by springs 39which are noticeably weaker than the spring 35 of slide valve 12. Thesprings 35, 36 and 39 are calibrated in such a way that their forces arein equilibrium when the slide valve 12 occupies the neutral positionshown in FIG. 1.

The shank 41 carries two cams 42 and 43, each of which is intended toco-operate with a respective one of the switches FC and FC referred toas end-of-travel switches, these cams 42 and 43 being mounted on saidshank 41 in such a way that, on the one hand, the two switches FC and FCinterposed in the electric control circuit in such a way as to controlthe excitation of electro-magnet EA of master slide valve 34, are openwhen the principal slide valve 12 is in its neutral position while, onthe other hand, one or the other of these of these switches PC and PC,is closed when the principal slide valve 12 occupies one of its extremepositions corresponding to the advance or return of the piston 2 of jack1.

The springs 39 are calibrated in such a way that the assembly of shank41 and cams 42 and 43 moves either at the same speed or at a slowerspeed than the armature A mass could also be added placement of theassembly 41, 42 and 43 with respect to that of the armature 37. At itsopposite end from electro-magnet EA the control shank 41 is furnishedwith a push button 46 which may, e.g., constitute the mass mentionedabove and which permits the manual actuation of principal slide valve12. The electromagnet EA the control shank 41, the bearings 44, theswitches FC and FC.,, and a part of the push button 46 are all housed ina casing 47 attached to one of the end faces of distributor 11.

The master slide valve 34 comprises, at one of its ends, a restrainingspring 48 which urges the master slide valve 34 into its extremeright-hand position, referred to as its neutral position, as shown inFIG. 1, which position permits the conduit 13 to communicate with thereturn circuit 14. This master slide valve 34 also carries, at its otherend, an electro-magnet EA which, when it is energized, displaces themaster slide valve 34 from its neutral position into a position where itprevents any communication between the conduit 13' and the returncircuit 14. The armature 50 of electro-magnet EA co-operates with, andserves as an abutment for, a control shank 51 guided in support bearings54 and carrying two cams 52 and 53, each of which co-operates with arespective one of the end-of-travel switches FC and FC At its oppositeend from electro-magnet AE the shank 51 is furnished with a push button56 which permits the manual actuation of master slide valve 34. Theelectro-magnet EA the control shank 51, the bearings 54, the switches FCand PC and a part of the push button 56 are housed in a casing 57attached to one end of master distributor 30. The shank 51 is urgedtowards the armature 50 by the springs 54 which are weaker than thespring 48 and which act against the push button 56, the springs 48 and54 being calibrated in such a way that the first master slide valve 34occupies, under the sole efl ect of their urging, the neutral positionshown in FIG. 1.

As in the case of the shank 41 of principal distributor 11, the shank 51of the first master distributor 30 could be furnished with a mass,constituted e.g. by the push button 56, which serves to decrease thespeed of displacement of the assembly 51, 52 and 53 with respect to thatof the armature 50.

The cams 52 and 53 are mounted on the shank 51 in such a way that theyalternately close their corresponding switches F0 and PC the switch FCbeing interposed in the electric control and monitoring circuit andbeing intended to control the energization and de-energization of one ofthe electro-magnets EA and EA of the principal distributor 11, while theother switch FC is connected to an audible or visual signalling device(not shown) and is intended to control said device in order to providean indication of the position of master slide valve 34.

The end-of-travel switches FC FC FC and F0 are closed when they areactuated by their respective cams 42, 43, 52 and 53, and open when theyare not contacted by said respective cams. Each cam 42, 43, 52 and 53comprises a wedge-shaped portion and a cylindrical portion. The cams 42and 43 are arranged on the control shank 41 and the cams 52 and 53 arearranged on the shank 51 in such a way that the cam 42 has itswedgeshaped portion directed towards electro-magnet EA the cam 52 hasits wedge-shaped portion directed towards the electro-magnet EA and thecam 43 has its wedge-shaped portion directed towards the push button 46and the cam 53 has its wedge-shaped portion directed towards the pushbutton 56.

I. The operation of the first embodiment of the shockresisting hydraulicdevice is as f0ll0ws.It should first be noted that the description ofthis operation only refers to the various hydraulic processes, and thatthe various processes of electrical control and monitoring of thedistributors will be described later in the present specification.

The positions of the principal and master slide valves 12 and 34,respectively, and of the piston 2 of jack 1 are as shown in FIG. 1. Thepump P is started up. The pump P supplies a hydraulic fluid to thedelivery circuit 7 13, this fluid passing through the return circuit 14to the inlet vat 15 and into the chambers 4 and 5 of jack 1, due to thefact that the principal slide valve 12 is in its neutral position. Thepressure of the fluid acting on either side of piston 2 is thuspractically equal to the atmospheric pressure.

(a) Displacement of the principal slide valve 12 to its extremeleft-hand position Electro-magnet EA is excited so that its armature 37pushes the slide valve 12 of distributor 11 towards the left in such away that communication between the delivery circuit 13 and the returncircuit 14 connected to the distributor 11 is interrupted, the chamber 5of jack 1 communicates with the delivery circuit 13, and the chamber 4of jack 1 communicates with the return circuit 14 mounted on saiddistributor 11. When the pressure in circuit 13 exceeds a certainpredetermined value, which is generally small, this pressure beingcalled the minimum operative pressure, the fluid acts on the lower faceof piston 17 of main pressure regulator 16 and urges said piston 17 andits valve 18 upward against the force exerted by restraining spring 22,the force produced by said spring 22 being relatively weak. In this way,the hydraulic fluid sent by the pump P through the delivery circuitpasses through orifice 19 of regulator 16 and through the return circuit14 to the inlet vat 15. The rest of the delivery circuit 13 and chamber5 of jack 1, although they are filled with fluid, are under practicallyno pressure, or in other words, are at the minimum operative pressure.

A part of the hydraulic fluid arrives at the first master distributor 30through the calibrated channel 24, the chamber 25a, the calibratedchannel 26 and the master conduit 13'. Because the chamber 33 of masterdistributor 30 is connected to the return circuit 14, in the case wherethe master slide valve 34 is in the position shown in FIG. 1, thisportion of the fluid also returns to the inlet vat 15. The pressureexisting in chamber 25a above piston 17 is thus practically equal to theatmospheric pressure and because the force generated by the fluiddelivered to chamber 25 and applied against the lower face of piston 17is greater than the opposing force of spring 22, the valve 18 remainsopen.

(b) Displacement of the master slide valve 34 towards the left Thedisplacement of the master slide valve 34 towards the left, in such away that the communication of the chamber 34 of master distributor 30with the return circuit 14 mounted on said distributor is interrupted,corresponds to a progressive augmentation of the fluid deliverypressure, or in other words, to a placing of the fluid under pressureuntil it attains a pressure called the maximum operative pressure. Tothis end, the electromagnet EA;, is excited with the result that itpushes the master slide valve 34 into its closing position against theopposing force of spring 48. The closing of the chamber 34 produces aprogressive increase in the pressure of the fluid contained in themaster conduit 13' and in the chamber 25a of the main regulator 16.

Since chamber 25a is then practically at the same pressure as thechamber 25 and the delivery circuit, the spring 22 progressively closesthe orifice 19, which operation is accompanied by a continuous increasein the pressure of the delivery fluid, which circulates without inducinghydraulic shocks on the piston 2 of jack 1.

(c) Advance of the piston 2 of jack 1 When a certain pressure, calledthe maximum operative pressure, has been established in the deliverycircuit 13 and in the chamber 5 of jack '1, the piston 2 advancestowards the right, i.e. towards the other end of jack 1. During thisdisplacement of piston 2 the fluid pressure remains constant; it doesnot begin to increase anew until the piston 2 has arrived at theright-hand end of its path of travel. This new increase in the fluidpressure is reflected against the lower face of piston 17 of regulator16 as well as in chamber 25a, channel 26 and conduit 13. The spring 28is adjusted in such a way that it permits, for a given pressure, theopening of retaining valve 27. As a result, a portion of the fluid inthe chamber 25a escapes towards the return circuit 14 through valve 26,chamber 29, channel 26a, space 21 and channel 23, and thus permits theopening of valve =18. The fluid delivered by the pump P then arrivesthrough the orifice 19 at the return circuit 14, but the maximumoperative pressure corresponding to the displacement of of the piston 2of jack 1 is maintained in the delivery circuit 13 and in the chamber 5.In this case, the valve 18 also plays the role of a maximum pressureregulator. However, the valve 18 is not necessarily combined with 'aregulatable retain ing valve 27 and a canal 26a, 23 communicating withthe atmosphere. The present invention may equally well be applied to thecase where a valve 18 is interposed in the delivery circuit 13 and wherethe upper chamber 25a of the valve is only connected to the returncircuit through the intermediary of a master distributor. In this case,any prior art type of maximum pressure regulator may also be provided inthe delivery circuit.

(d) Displacement of the master slide valve 34 towards the right Thedisplacement of the master slide valve 34 towards the right, in such away as to permit the communication of the chamber '33 of masterdistributor 30, and thus of the master conduit 13', with the returncircuit 14 fastened to said distributor 30, corresponds to a progressivedecrease in the pressure of the fluid contained in the delivery circuit13 and in the chamber 5 of jack 1. In other words, this corresponds to aprogressive removal of pressure from the delivered fluid. In efiect,when the master slide valve 34 connects the chamber 25a, situated abovepiston -17 of regulator 16, to the return circuit 14 through theintermediary of channel 26, master conduit 13' and chambers 31, 32 and33 of master distributor 30, the fluid contained in this chamber 25aescapes progressively towards the return circuit '14. As a result, thevalve 18 can open wide in proportion to the quantity of fluid drivenfrom the chamber 25a through the channel 26 of regulator 16. A minimumoperative pressure then exists in the delivery circuit 13 and in thechamber 5 of jack 1.

(e) Displacement of the principal slide valve 12 towards the right toits neutral position 'Electro-magnet EA is deactivated, which permitsspring 35 to return the main slide valve to its neutral position, inwhich position the delivery circuit 13, the return circuit 14, and thechambers 4 and 5 of jack 1 are all interconnected through theintermediary of chambers 8, 9 and 10 of principal distributor 11. As aresult, the pressure of the fluid contained in the chambers 4 and 5 andthe circuit 13 is equal to the atmospheric pressure.

(f) Displacement of the principal slide valve 12 towards its extremeright-hand position Electro-magnet EA is excited so as to cause itsarmature 38 to push the slide valve 12 towards the right in such a waythat the communication between the delivery circuit 13 and the returncircuit 14 attached to distributor 11 is interrupted, the chamber 4 ofjack 1 is connected to the delivery circuit 13, and the chamber 5 ofsaid jack 1 is connected to the return circuit 14 through theintermediary of the conduit 7 of the chamber 9 of principal distributor11. The fluid contained in the delivery circuit 13 and in the chamber 4is at the minimum operative pressure since the valve 18 opensautomatically.

9 (g) Displacement of the master slide valve 34 towards the left Thedisplacement of the master slide valve 34 towards the left in such -away as to break the communication between the chamber 33 and the returncircuit 14 attached to the distributor 30 corresponds, as has alreadybeen said, to a progressive placing under pressure of the fluidcontained in the delivery circuit 13 and in the chamber 4 of jack 1. Thedifierent phases of this operation have already been described inparagraph Ib, above.

(h) Return of piston 2 of jack 1 When the maximum operative pressure hasbeen established in the delivery circuit 13 and in the chamber 4, thepiston 2 returns to the left. This process is practically identical withthat described in paragraph Ic, above.

(i) Displacement of the master slide valve 34 towards the right Thiscorresponds to a progressive decrease in the pressure of the fluidcontained in the delivery circuit 13 and in the chamber 5 until aminimum operative pressure has been established. This process isidentical with that described in paragraph Id, above.

(1') Displacement of the principal slide valve 12 towards the left toits neutral position The electro-magnet EA is deactivated, which permitsthe spring 36 to push the principal slide valve 12 into its neutralposition, in which position the delivery circuit 13 as Well as thechambers 4 and 5 of jack *1 are all interconnected together and to thereturn circuit 14 and are, as a result, placed in communication with theatmosphere.

In order to permit a programming of the operative pressure so as tocause it to comprise one or several intermediate pressures between theminimum operative pressure and the maximum operative pressure, thepresent invention also provides one or several master distributors,identical with that shown in FIG. 1.

Turning now to FIG. 2, the hydraulic anti-shock device comprises twomaster distributors 30 and 58. In this case, a second master conduit'13" is branched ofi of the first master conduit 13' between the outputof pressure regulator 16 and the first master distributor 30. Thisconduit 13" is connected to a second master distributor 58 which,through the intermediary of an auxiliary pressure regulator 59interposed in the return circuit 15 attached to said distributor 58,communicates with the inlet vat 15 of pump P.

This auxiliary pressure regulator 59 comprises a piston 65 whose lowerface is furnished with a valve 66 adapted to close an orifice 67 towhich is attached a portion of the return circuit 14. A restrainingspring 68 suitably calibrated and acting on the upper face of piston 65urges valve 66 into its closed position.

The second master distributor 58 also comprises, at each end, arespective one of chambers 69 and 70 in permanent communication with thereturn circuit 14, and a central chamber 71 into which empties thesecond master conduit 13". This distributor 58 is furnished with adouble-piston master slide valve 64 which, in its intermediate position,prevents any communication of the second master conduit 13" and thecentral chamber 71 with the end chambers 69 and 70 of said distributor58 and thus with the return circuit 14.

The second master slide valve 64 carries at one of its ends arestraining spring 72 which urges the slide valve 64 into its extremeright-hand position, called the neutral position, as shown in FIG. 2,and permits communication between the conduit 13" and the return circuit14 through the intermediary of chambers 69, 70 and 71 of masterdistributor 58.

At its other end, the master slide valve 64 carries an electro-magnet EAwhich, when it is activated, displaces the master slide valve 64 fromits neutral position to a position, called the intermediate position,where it blocks communication between the second master conduit 13" andthe return circuit 14. The armature of electromagnet EA co-operateswith, and serves as an abutment for, a control shank 61 guided insupport bearings 74 and carrying two cams 62 and 63, each of whichco-operates with a respective switch F0, and PC marking the ends of thepath of travel of the shank. At the opposite end from electro-magnet EAthe shank 61 is furnished with a push-button 75. The elements EA 61, 62,63, 75, PC and PC as in the case of the first master distributor 30, arehoused in a casing 76 fastened to the side surfaces of the second masterdistributor 58.

Shank 61 is urged towards the armature 61} by springs 73, which areweaker than the spring 72 and which act on the push button 75. Springs72 and 73 are calibrated in such a way that the second master slidevalve 64 occupies, when exclusively under their influence, the neutralposition shown in FIG. 2. As in the case of shanks 41 and 51 ofdistributors 11 and 30, respectively, the shank 61 of the second masterdistributor 58 can be furnished with a mass, constituted e.g. by pushbutton 75, so as to decrease the displacement speed of the assembly 61,62 and 63 with respect to that of the armature 60 and of the masterslide valve 64.

The switch PO, is open and the switch FC is closed when they areactivated by their respective cams 63 and 62. The cams 62 and 63 aremounted on the shank 61 in such a way that they control, orsimultaneously permit, the opening, or the closing, of switches F0 andFC The switch FC which is connected to a signalling device, is closedand controls the emission of a luminous or acoustic signal when thesecond master slide valve 64 breaks the hydraulic connection between themain regulator 16 and the auxiliary regulator 59, while the switch FCinterposed in the electric command and monitoring circuit, is open anddisconnects the excitation of electromagnet EA of the first masterdistributor 30 when the slide valve 64 of the second master distributor58 is in its neutral position, i.e. when the latter establishes ahydraulic connection between the regulators 16 and 59.

It should also be noted/that in the case of a hydraulic anti-shockdevice having two master distributors, the switch FC marking one end oftravel in the first master distributor 31 no longer controls a luminousor audible signalling device, but this switch is interposed in theelectric control and monitoring circuit of the hydraulic anti shockdevice and is particularly intended to only permit the actuation of theelectro-rnagnet EA of the second master distributor 58 when it isclosed, i.e. when the first master slide valve 34 breaks thecommunication between the principal pressure regulator 16 and the returncircuit 14 attached to the first master distributor 30.

II. The operation of this embodiment of a hydraulic anti-shock device isas f0llows.-As before, the description of this operation only concernsthe various hydraulic processes effectuated by the device of the presentinvention. The positions of the principal slide valve 12 and the masterslide valves 34 and 64, as well as those of the pressure regulators 16and 59 are as shown in FIG. 2. When the motor M is placed in operation,the pump P supplies hydraulic fluid to the delivery circuit 13, thisfluid passing through the return circuit 14 attached to the principaldistributor 11 and through the chambers 4 and 5 of jack 1, since theprincipal slide valve 12 is in its neutral position (FIG. 3). As aresult, the pressure of the fluid acting on both sides of the piston 2of jack 1 is substantially equal to atmospheric pressure.

(a) Displacement of the principal slide valve towards its extremeleft-hand position The electro-magnet EA is excited so that its armature37 pushes the slide valve 12 of distributor 11 towards the left. Theseoperations and the eilects thereof have already been described inparagraph Ia. The fluid passing through the channel 26 of main regulator16 arrives not only at the first master distributor 30, and from thereto the return circuit 14, but also at the second master distributor 58and its return circuit 14. However, the auxiliary regulator 59 does notpermit the fluid passing through the second master distributor 58 toflow into the inlet vat 15, since valve 66 is closed.

([2) Displacement of the first master slide valve 34 towards the leftWhen the electro-magnet EA of the first master distributor 30 isexcited, its armature 50 pushes the master slide valve 34 towards theleft in such a way as to cause an interruption of the communicationbetween the chamber 33 and the return circuit 14 attached to the firstmaster distributor 30. As has already been described in paragraph 'Ib,there is then established in the chamber 25a of the main regulator 16 acertain counter-pres sure applied against the upper face of piston 17which, by acting on the valve 18, determines progressively, and withoutproducing hydraulic shocks, the establishment of a pressure, called theaverage operative pressure, in the delivery circuit 13 and in thechamber of jack 1. This average pressure is determined by the spring 68of auxiliary regulator 59. From the moment when this average pressure isexceeded in the delivery circuit 13, the valve 66 of auxiliary regulator59 opens and creates a pressure drop in the chamber 25a of mainregulator 16, so that its valve 18 also opens and leads the pressure ofthe fluid in the delivery circuit to arrive at the average operativepressure.

(c) Displacement of the second master slide valve 64 towards the leftThis displacement, produced by the actuation of electro-magnet EA of thesecond master distributor 58, places the slide valve 64 in a position inwhich the communication between the central chamber 71 of saiddistributor and the return circuit 14 is interrupted. This causes aprogressive increase in the pressure of the delivery fluid, commencingfrom the average operative pressure and terminating at the maximumoperative pressure. This process is similar to that described inparagraph Ib.

(d) Advance of the piston 2 of jack 1 The piston 2 advances under theeffect of the maximum operative pressure which is applied thereagainst(see paragraph 16).

The processes for removing the pressure from the delivery circuit 13 andthe chamber 5 of jack 1, for the reversal of the movement of principalslide valve 12, for the placing under pressure of the chamber 4 of jack1, for the return of piston 2 of jack 1, for the removal of pressurefrom the delivery circuit 13 and the chamber 4, and for the displacementof principal slide valve 12 into its intermediate position, are similarto those described in paragraphs Id to If, above.

The only essential difference consists in the fact that theestablishment of the maximum operative pressure and the removal ofpressure are carried out in two steps, but these operations are alwaysprogressive.

In order to place the delivery circuit under pressure, in order tocontrol either the advance or the return of the piston 2 of jack 1, thefollowing operations are carried out in the following order:

Displacement of the principal slide valve 12 from its neutral positionto an extreme position, corresponding to the advance or return of piston2;

Displacement of the master slide valve 34 into its closing position;

And displacement of the second master slide valve 64 into its closingposition.

After the advance or return of jack-piston 2, the system is caused tooperate in an inverse fashion in first returning the second master slidevalve 64, then the first master slide valve 34, and finally theprincipal slide valve 12 to their neutral positions.

For the control and monitoring of the activation and the de-activation,several electric circuit arrangements are provided which permit either asemi-automatic control or an entirely automatic control of the hydraulicanti-shock device.

Turning now to FIG. 3, the electric control and monitoring circiut forthe hydraulic anti-shock device shown in FIG. 1 comprises several groupsG G G G G and G of electric elements, these groups being energized inparallel by a single-phase alternating current source In this figure,there is also shown, schematically, the motor M of pump P, this motorbeing exicted by a threephase mains RT.

In a general manner, the various contacts and switches shown in FIGS. 3,4 and 5, are of two dilferent types. Assuming that a current flowsthrough the system of FIG. 3 in the sense of the arrow F, all of thecontacts and switches to the left of the direction of curent flow in theconductors with which they are associated are open when they are notactivated by their respective control organs or, on other words, whentheir corresponding relays are not actuated or when they are notdepressed by their corresponding cams. Similarly, the contacts andswitches to the right of this direction of current flow are closed whenthey are not actuated by their respective control organs. The contactscontrolled by the same relay are indicated by the same main reference,but each bears a difierent sufi'ix.

In FIG. 3, the first group of electrical elements G comprises a relay Ccalled the control switch for motor M; this relay C is mounted in serieswith a manual control switch Mm which is generally open so as to permitthe starting of motor M, and with another manual control switch Am whichis normally closed, permitting the stopping of motor M.

A contact C called the holding contact for relay C is connected inparallel across the terminals of switch Mm, a second contact C of relayC is interposed in the line L feeding the other groups G to G and athird group C of three contacts is placed in the lines supplying energyto motor M, these contacts C C and the three contacts C being closedwhen their relay C is actuated.

The second group of electrical elements G comprises two relays R and Rcalled relays for monitoring the advance and return of the piston jack,mounted in parallel with one another. A manual switch DCAV, referred toas the switch for starting the advance cycle, is mounted in parallelwith a contact R referred to as the holding contact foradvance-monitoring relay R the switch DCAV and the contact R being eachmounted in series with said relay R Another manual switch DCAR, referredto as the switch for starting the return cycle, is mounted in parallelwith a contact R referred to as the holding contact for thereturn-monitoring relay R this contact R and the switch DCAR each beingmounted in series with the relay R A third manual switch Ac, called thecycle-stopping switch, is normally closed and is mounted in series withthe contacts R R and the switches DCAV and DCAR, the contacts R and Rclosing when their corresponding relays R and R are actuated.

The third group of electrical elements G comprises a relay, called theadvance-control relay C the winding of the first electro-magnet EA ofthe principal slide valve 12, and a first contact C which is normallyopen and which is operated by said relay C this contact C and thiswinding EA being mounted in series with one another, but in parallelwith respect to said relay C As shown in FIG. 3, the winding EA isconnected across the terminals of relay C through the intermediary ofcontact C which, in the present case, is not indispensable. However, theseries connection of contact C and winding EA could also be connectedbetween the lines L and L, in parallel with relay C without beingdirectly connected across the terminals of said relay C The precedingconsiderations are, in addition, also valid for the connection of thewindings of the other electromagnets EA EA and EA and for theircorresponding control relays.

The third group G, also comprises a second contact C which is normallyclosed, is mounted in series with relay C and is controlled by the relayC of the fifth group G a third contact R which is normally closed, ismounted in series with the contact C and is controlled by the relay R ofthe sixth group G a fourth contact R which is normally open, is mountedin parallel with the contact R and is controlled by theadvance-monitoring relay R a fifth contact R which is normally open, ismounted in series with the contact R but in parallel with the contact Rand is controlled by the relay R and a sixth contact, called a holdingcontact C which is normally open, is mounted in parallel with thecontact R and is commanded by the relay C The fourth group of electricalelements 6,; comprises a relay C referred to as the control relay forthe first distributor 30; the winding of electro-magnet EA of masterslide valve 34; a first contact C which is normally, open, this windingEA and contact C being mounted in series with one another and inparallel with relay C a second and a third contact R and R respectively,both of which are normally open and which are mounted in parallel withone another and in series with relay C the contact R being controlled bythe relay R and the contact R being controlled by the relay R and thetwo switches FC and FC each of which is associated with a respective oneof the ends of the path of travel of the movable element of distributor11, each of these switches co-operating with a respective one of thecams 42 and 43 mounted on the shank 41 of principal slide valve 12,these switches FC and PG; being mounted electrically in parallel withone another, but in series with the contacts R and R 2, and beingnormally open when they are not acted upon by their corresponding cams42 and 43.

The fifth group of electrical elements G comprises: a relay C referredto as the return-control relay, the winding of the second electro-magnetEA of the principal slide valve 12; a first contact C which is normallyopen and which is controlled by the relay C this Winding EA and thiscontact C being mounted in series with one another but in parallel withrelay C a second contact C which is normally closed, mounted in serieswith said relay C and controlled by the relay C of the third group G athird contact R which is normally closed, mounted in series with contactC and controlled by the relay R of the sixth group G a fourth contact Rwhich is normally open, mounted in parallel with the contact R3 andcontrolled by the return-monitoring relay R a fifth contact R which isnormally open, mounted in series with the contact R but in parallel withthe contact R and controlled by the relay R and a sixth contact, calledthe holding contact C which is normally open, mounted in parallel withthe contact R and controlled by the relay C The sixth group ofelectrical elements G comprises: a relay R referred to as the maximumoperative pressure monitoring relay, mounted in series with the switchFC which is responsive to the end of travel of the movable elements ofmaster distributor 30, this switch being closed when it is acted on byits corresponding cam 53, Le. when the master slide valve 34 is in itsneutral position.

A manual switch, called the emergency switch Au, is also interposed inthe supply line L feeding the various groups of electrical elements.

III. The above described electrical circuit functions in combinationwith the hydraulic anti-shock device of FIG.

1 in the following manner.This description concerns particularly theorder of the various electrical control operations of the device of thepresent invention, which operations relate to the various hydraulicphenomena described earlier in this specification.

All of the switches and contacts are initially in the positions shown inFIG. 3. These positions correspond to those of slide valves 12 and 34 asindicated in FIG. 1.

(a) The starting of motor M of pump P The switch Mm is closed. The relayC is then actuated and closes the switches C C and C The relay C remainsactuated when the switch Mm is opened, since the holding contact Cremains closed. Because the switch C is closed, the motor M is suppliedwith current. The switch C being closed, as is the end-of-travel switchPC the relay R is actuated and its contacts R and R are opened while itscontacts R and R close. When the contacts R and R on the one hand, and Rand R on the other hand, are opened, the relays C and C cannot beactuated.

(b) Control of the electro-magnet EA of principal slide valve 12 Thiscontrol corresponds to a displacement of the principal slide valve 12towards the left (FIG. 1). To this end, the switch DCAV is closed inorder to permit the actuation of relay R thereby controlling the closingof its contacts R R and R After the opening of switch DCAV, theactuation of relay R is maintained due to the fact that its holdingcontact R is closed.

The relay C is then supplied with current through the intermediary ofclosed switches R R and C The actuated relay C closes its holdingcontact C as well as the contact C this latter contact thus permittingthe actuation of electro-magnet EA so as to permit it to displace theprincipal slide valve 12 towards the left.

(0) Control of the electro-magnet EA for the first master slide valve 34This control corresponds to a displacement of the slide valve 34 towardsthe left and to the causing of a progressive increase in pressure of thefluid contained in the delivery circuit 13 and in the chamber 5 of jack1.

The control shank 41 of the principal distributor 11 follows thedisplacement of slide valve 12 towards the left so that the cam 42 movesto close the switch FC The relay C is then supplied with current throughthe intermediary of the switch PC and the switch R both of which areclosed. The relay C closes the contact C and thus permits the actuationof electro-magnet EA which urges the master slide valve 34 towards theleft.

The control shank 51 follows the displacement of master slide valve 34.The cam 53 moves away from the switch FC permitting the switch to open,and the cam 52 closes the switch FC when the slide valve 34 has reachedits closing position. An audible or visual signal, controlled by theswitch FC indicates this position of slide valve 34. However, priorthereto, the switch FC has disconnected the supply of current to relay Rso that its contacts R and R re-open, and its contacts R and R close.

Electro-magnet EA remains actuated since the relay C is supplied withcurrent through the intermediary of the closed contacts C R andC On theother hand, the relay C controlling the actuation of electro-magnet EAcannot be supplied with current, despite the closing of contact Rbecause the contact C remains open as long as the relay C is actuated.

The piston 2 of jack 1 advances towards the right-hand end of its pathof travel under the effect of the maximum operative pressure. It shouldalso be noted that follow each other automatically.

(d) Termination of the advance cycle of piston 2 The end of the advancecycle corresponds to successive de-actuations of the electro-magnets EAand EA i.e. to the progressive reduction in pressure in delivery circuit13 and in the chamber 5 of jack 1.

T this end, the switch Ac is momentarily opened so as to disconnect thesupply of current to relay R causing the contacts R R and R thereof tore-open. The relay C remains actuated through the intermediary of closedcontacts R and C When the contact R opens, the relay C is de-energized,the contact C opens and the electro-magnet EA is de-energized. Themaster slide valve 34 is then urged to its neutral position by thespring 48. Due to this fact, the switch FC opens and the switch FC thencloses and permits a re-energization of the relay R causing the openingof contact R and, as a result, the de-energization of relay C Thecontact C opens and the electro-mag'net EA is de-energized. The springthen urges the principal slide valve 12 into its neutral position,causing the cam 42, which follows this movement, to move away from theswitch FC permitting the latter to open.

(e) Control of the electro-magnet EA of principal slide valve 12 Thiscontrol corresponds to the displacement of slide valve 12 towards theright and to the preparation for the return of piston 2 of jack 1.

The switch DCAR is closed, permitting the energization of thereturn-monitoring relay R the contacts of which R R and R also close.Owing to its holding contact R the relay R remains energized after therelease of switch DCAR.

The relay C is then energized through the intermediary of the closedcontacts R R and C The contact C closes and permits the energization ofelectro-magnet EA which urges the principal slide valve 12 towards theright.

(f) Control of the electro-magnet EA 3 of master slide valve 34 Thiscontrol corresponds to the displacement of slide valve 34 towards theleft and to the progressive increase in pressure of the fluid in thedelivery circuit and in the chamber 4 of jack 1.

The control shank 41 of the p rincipal distributor 11, under the efiectof electro-magnet EA displaces towards the right and the cam 43 closesthe switch FC The relay C is then energized through the intermediary ofthe switch F0 and the closed contact R The energization of relay C3closes the contact C energizing electro-magnet EA The process whichfollows is then the same as that described in paragraph III (c).

The control shank 41 of the principal distributor 11,

(g) Termination of the return cycle of piston 2 The end of the cyclecorresponds to the successive deenergizations of electro-magnets EA andEA as well as the progressive reduction of pressure in the deliverycircuit 13 and the chamber 4 of jack 1.

The switch Ac is momentarily opened, causing the deenergization of relayR and the resulting re-opening of contacts R R and R of this relay. Therelay C remains energized through the intermediary of the closedcontacts R and C but the relay C becomes de-energized because of theopening of contact R The electromagnet EA is therefore de-energizedsince the contact C also re-opens and the spring 48 urges the cam 53against the switch FC which closes the switch and thus permits there-excitation of relay R The contacts R and R open and the relay Cbecomes de-energized, as does the electro-magnet EA The spring 36 thenurges the principal slidevalve 12 into its neutral position and the cam43 of the shank 41 follows this movement under the influence of springs39 and moves away from switch FC In case of emergency the apparatus canbe turned off by the switch Au.

It might be desirable to automatically control the stopping of theadvance cycle, the reversal of the principal slide valve, the return ofthe piston 2 and the stopping of the return cycle.

For this purpose, in accordance with the present invention, there isprovided on the shank 3 of the jack-piston 2 a cam which. is adapted toco-operate alternately with two switches FC and FC referred to asswitches for monitoring the ends of the advance travel and the returntravel, respectively, of piston 2, this co-operation taking place whenthe piston 2 of jack 1 is in one of its extreme positions in such a waythat the end-of-advance travel monitoring switch FC through theintermediary of the electric circuit, controls the de-energization ofthe electro-magnet EA of the first master slide valve 34, then thede-energization of the first electro-magnet EA then the energization ofthe second electro-magnet EA; of the principal slide valve 12, and thenthe re-energization of the electro-magnet EA while the end-of-returntravel monitoring switch FC controls, also through the intermediary ofthe electric circuit, the de-energization of the electro-magnet EA ofthe master slide valve 34, then that of the second electro-magnet EA ofthe principal slide valve 12.

When the shank 3 of jack-piston 2 is adapted to selectively operate,through the intermediary of its cam 80, the two switches FC and FC theelectric control and monitoring circuit comprises, in addition twogroups of supplementary electrical elements G and G mounted in parallelwith the other groups, while the group G comprising the advance andreturn monitoring relays R and R is modified.

As shown in FIG. 4, the electric circuit, fed by the three-phase mainsRT, through the itermediary of a single-phase transformer Tr, comprisesin addition to groups G to G a group G constituted by a relay R referredto as the end-of-advance travel and reversal monitoring relay, thisrelay R being mounted in series with the switch FC said switch beingnormally open when it is not acted on by the cam 80; and an eighth groupG consituted by a relay R referred to as the endof-return travelmonitoring relay, mounted in series with the switch FC this switch beingnormally open when it is not acted on by the cam 80.

The group G comprises, in addition to the elements shown in group G ofFIG. 3, normally closed contact R connected in series on the one handwith relay R and the contact R and on the other hand with the switch Dc,referred to as the cycle-starting switch. This annual switch Dccorresponds moreover to the switch DCAV of FIG. 3. In the circuitassociated with the relay R in place of the manual return-cycle-startingswitch, there are provided four contacts C R R and R the first contact Cbeing normally closed and being controlled by the advance-control relayC the second contact R being normally closed and being commanded by themonitoring relay R the third contact R being normally closed and beingcontrolled by the advance monitoring relay R and the fourth contact Rbeing normally opened and being controlled by the end-of-advance travelmonitoring relay R the two contacts R and R being mounted in paralleland the two contacts R and C in the immediate vicinity of relay R beingmounted in series with the holding contact R of relay R The manualswitch Ac, as in the preceding circuit, is mounted in series with all ofthe other contacts and relays of the group G IV. The operation of theelectric circuit provided for a hydraulic anti-shock device having amaster distributor and permitting the automatic control of a completework cycle of the piston 2 is as follows.All of the contacts andswitches are initially in the positions shown in FIG. The positionscorrespond to those of the slide valves 12 and 34 as indicated in FIG. 1and' correspond to the state of the complete device when it is at rest(including the stoppage of pump P).

A. Starting of the motor M and the pump P.This starting is eifectuatedin the manner described above in paragraph IIIa.

B. Automatic control of a complete cycle of piston 2.The variousprocesses carried out during the course of a complete cycle serve toinitiate one another, but for the sake of clarity these processes willbe described below as separate phases of operation.

(a) Control of the electro-magnet EA of the principal slide valve 12 Theswitches RT are permanently closed. Starting switch Mm is closed,causing the energization of relay C through the intermediary of normallyclosed switch Au, normally closed switch Am and switch Mm. Energizedrelay C closes holding contact C motor-energizing contact C andcircuit-power-supply contact C Because of the closure of holding switchC the relay C will remain closed even after the opening of switch Mm.The switch Dc is momentarily closed, thereby energizing relay R throughthe intermediary of contact R The energization of relay R opens contactR thereby preventing any energization of relay R as long as relay R isenergized.

The energization of electro-magnet EA is then effectuated in the mannerdescribed in paragraph IIIb.

Because relay C is energized, the cont-act C opens and prevents anyenergization of the return-travel monitoring relay R Similarly, thecontact R is open when the relay R is energized, thereby preventing anyenergization of the relay R when the switch F is closed, i.e. when thepiston 2 is in its extreme left-hand position.

(b) Control of the electro-magnet EA of the first master slide valve 34This operation is identical to that described in paragraph Illc. Thepiston 2 advances towards the extreme right-hand side of jack 1 underthe influence of the maximum operative pressure and the cam 80 movesaway from the switch FC permitting this switch to open. As a result, therelay R is de-energized and the contact R re-closes, but the relay Rremains in its de-energized state, since the contacts C R R and R arestill open.

(c) Automatic stopping of the advance cycle of piston 2 When the piston2 arrives at the end of its advance travel, the cam 80 closes the switchFC causing the relay R to be energized. Due to this fact, the contact Ropens, the relay R becomes de-energized, and the contacts R R and Rre-open, but on the other hand, the contact R re-closes.

The procedures by which the electro-magnets EA and EA are successivelyde-energized is the same as that described in paragraph IIId.

(d) Control of the eIectro-magnet EA of the principal slide valve 12,corresponding to a reversal of the principal slide valve 12 Because therelays R and R are no longer energized while the relay R is energized,the contacts R R and R are closed and when the relay C is de-energized,the contact C re-closes, thereby permitting the energization of relay RThe rest of this procedure is identical with that described in paragraphIIIe.

(e) Control of the electro-magnet E11 of the master slide valve 34 Thisprocedure is identical with that described in paragraph IIIf. However,when the piston 2 commences to return, the cam 80 moves away from theswitch FC interrupting the supply of current to the relay R so thatcontact R recloses and contact R re-opens. The opening of contact R doesnot affect the energization of relay R since this contact R is inparallel with the holding contact R which remains closed as long asrelay R is energized.

(f) Automatic halting of the return cycle of piston 2 I At the end ofthe return travel of piston 2 the cam closes the switch FC so that therelay R is energized. Its contacts R opens and the relay R becomesdeenergized. The remainder of this procedure is identical to thatdescribed in paragraph IIIg.

FIG. 5 shows an electrical circuit permitting the auto matic control ofa complete cycle (advance, reversal and return of the piston 2, and theprogressive increase or decrease of pressure between each of theprocedures) of the piston 2 of jack 1 furnished with a hydraulicantishock device having two master distributors 30 and 58, as shown inFIG. 2.

In this case, the energization of the various electromagnets EA, each ofwhich is mounted in series with its respective control contact but allof which are mounted in parallel with one another, is assured by asingle-phase transformer Tr connected across the mains RT in parallelwith the transformer Tr feeding the various relays R and C mounted inparallel with respect to one another. It thus results that theelectro-magnets EA are mounted in parallel with their correspondingrelays C, as is true for the systems shown in FIGS. 3 and 4.

The electric circuit for a hydraulic anti-shock device having two masterdistributors, of the type shown in FIG. 2, is characterized in that itcomprises in addition to the groups of circuits shown in FIG. 3(permitting a semiautomatic control of the advance and return cycles) orof the circuit of FIG. 4 (permitting an automatic command of a completecycle): a group of electrical elements G adapted to control theenergization and the de-energization of the electro-magnet EA of thesecond master slide valve 64, as well as an end-of-travel switch FCF,provided in group G this switch being controlled by the second masterslide valve 64 and being adapted to disconnect the energizing current tothe electro-magnet EA of the first master slide valve 34 when the secondmaster slide valve 64 has returned to "its neutral position.

The switch FC7 is mounted in parallel with the contacts R and R one ofthe terminals of this parallelarrangement also being connected to therelay C while the other terminal thereof is connected to the parallelarrangement of switches FC and FC The switch F07 is open when it isacted on by the cam 63 rigidly connected to the control shank 61 of thesecond master distributor 53. The opening of the switch FC correspondsto the neutral position of the second master slide valve 64. e

The group of electrical elements G is constituted by a relay C referredto as the control relay for the second master distributor 58, by thewinding of the electromagnet EA of the second master slide valve 64, bya contact C which is normally open and which is controlled by the relayC this winding EA, and this contact C being mounted in series with oneanother but in parallel with respect to the relay C Group 6,, alsocomprises the end-of-travel switch FC of the first master distributor30, this switch FC being operated by the cam 52 of shank 51 so as to beclosed when acted on by this cam when the first master slide valve 34 isin its neutral position, assuring communication between the principalpressure regulator 16 and the return circuit 14 attached to saiddistributor 30. Group G further comprises two contacts R and R both ofwhich are normally open and are mounted in parallel with one another andin series with the relay C through the intermediary of switch FC thecontacts R being controlled by the controlled by the return-controlrelay R V. The operation of the electric circuit provided for ahydraulic anti-shock device having two master distributors andpermitting the automatic control of a complete work cycle of the piston.2 is as follows.-All of the contacts and switches are initially in thepositions shown in FIG. 5. These positions correspond to those of theslide valves 12, 34 and 64, as indicated in FIG. 2 when the apparatus isat rest, the pump P also being at rest.

A. Starting the motor M and the pump P.-This starting is eifectuated inthe same manner as that described in paragraph IIIa, above.

B. Automatic control of a complete cycle of piston 2.- The variousoperations effectuated during the course of a complete cycle serve totrigger one another, but for the sake of clarity these procedures willbe described as separate phases of operation.

(a) Control of the electro-magnet EA of principal slide valve 12 Thisprocedure is identical with that described in paragraph IVB-a, exceptthat the relay R when energized, also closes the contacts R (b) Controlof the electro-magnet EA first master slide valve 43 When the energizedelectro-magnet EA displaces the slide valve 12 towards the left, thecontrol shank 41 follows this movement and the cam 42 closes the switchF0 Since the contact R has been previously closed, the relay C isenergized and closes the contact C with the result that theelectro-magnet EA is also energized. As a result, the master slide valve34 is urged into its closed position, which corresponds to theprogressive establishment of the average operative pressure in thedelivery circuit 13 and in the chamber of jack 1.

(c) Control of the electro-magnet EA, of the second master slide valve64 When the first master slide valve 34 is displaced towards the left,the shank 51 follows this movement and its cam 52 closes the switch FCBecause the energization of relay R had previously closed the contact Rthe relay C is energized. The contact C closes, and thereby permits theenergization of the electro-magnet HA causing the latter to urge thesecond master slide valve 46 towards the left into its closing position.There is then produced a progressive increase in the pressure in thedelivery circuit 13 and in the jack-chamber 5 until the maximumoperative pressure is reached, which pressure controls the advance ofpiston 2 towards the right-hand end of jack 1. The shank 61 follows thedisplacement of the second master slide valve 64 so that, firstly, itscam 63 separates from switch FC causing the switch to close, and then,when the slide valve 64 is in its closed position, the cam 62 closes theswitch FC so as to control the emission of an audible or visible signal.Because the piston 2 advances towards the right-hand end of jack 1, thecam 80 separates from the switch FC permitting this switch to open. Therelay R is thus de-energized and the contact R re-closes.

(d) Automatic termination of the advance cycle of piston 2,corresponding to a successive de-energization of the electro-magnet EAEA and EA This procedure corresponds to a progressive reduction in thepressure of the fluid in the delivery circuit 13 and the chamber 5.

When the piston 2 arrives at the end of its forward travel path, the cam80 closes the switch FC and the relay R is energized, causing itscontact R to open. As a result, the relay R is de-energized, its contactR re-closes and its other contacts R R R and R reopen. Relay C remainsenergized because contacts R and C remain closed due to the fact thatrelays R and R are not energized. The relay C remains energized throughthe intermediary of the closed switches FC and PC7- But the relay Cbecomes de-energized because the contact R has opened and the contact Rhas not closed.

The contact C re-opens and the electro-magnet EA, is tie-energized,thereby permitting the spring 72 to urge: the second master slide valve64 into its neutral position, which corresponds to a progressive returnto the average operative pressure in the delivery circuit 13 and in thechamber 5 of jack 1. When the master slide valve 64 is urged towards theright, the cam 62 frees the switch FC which opens, then the cam 63 opensthe switch FC7.. As a result, the relay C is de-energized, the contact Copens, and the electro-magnet EA;, is de-energized, thus permitting thespring 48 to urge the first master slide valve 34 into its neutralposition (progressive return to the minimum operative pressure).

The shank 51 is also urged towards the right so that the cam 52 permitsthe opening of switch FC and so that the cam 53 then re-closes theswitch FC so as to thus permit the energization of relay R As a result,the contacts R and R re-close while the contacts R and R re-open. Theenergization of relay C is then disconnected'by the contact R causingthe contact C to open and the electro-magnet EA to be de-energized, withthe result that spring is permitted to urge the principal slide valve 12towards the right into its neutral position (progressive elimination ofpressure). On the other hand, the contact C closes. The shank 41 followsthis movement and the cam 42 frees the switch FC permitting this switchto re-open.

(e) Automatic control of the return cycle of piston 2, corresponding toa reversal of the principal slide valve 12 and the successiveenergization of electro-magnets E142, EA3 and E144.

This procedure corresponds to a progressive creation of pressure in thedelivery circuit 13 and the chamber 4 of jack 1.

The contacts R and R are closed since their corresponding relays R and Rare not energized. The contact R is closed since the switch P0 is closedwhile the relay R is energized.

When the relay C is de-energized (see paragraph VB-d), the contact Ccloses and the relay R is energized. Its contacts R R R and R close and,because the relay R is energized (see paragraph VB-d) the contact R isclosed. The contact C is also closed (see paragraph VB-d). The relay Cis then energized through the intermediary of the closed contacts R Rand C The contact C closes and permits the energization of theelectro-magnet EA which urges the principal slide valve 42 from itsneutral position towards its extreme right-hand position. The shank 41is also displaced in this direction and its cam 43 closes the switch PC,which, through the intermediary of closed contact R permits theexcitation of relay C The contact C closes and permits the excitation ofthe electro-magnet EA of the first master distributor 30, the slidevalve 34 of which is urged towards the left. This corresponds to theprogressive establishment of the average operative pressure in thedelivery circuit 13 and in the chamber 4 of jack 1.

The shank 51 follows this movement. The cam 53 permits the opening ofthe switch FC and the de-energization of the relay R As a result, thecontacts R and R re-close and the contacts R and R re-open.

The relay C continues to be energized through the intermediary either ofthe closed contacts C R and R or of the closed contacts R and C Therelay C cannot be energized since the contact C is open, due to the factthat the relay C is energized.

Then, when the slide valve 34 occupies its closed position, the cam 52closes the switch F0 so that the relay C can be energized through theintermediary of tlns switch and of the closed contact R The contact C 21closes and the electro-magnet EA; is energized; the latter then urgesthe second master slide valve 64 into its closed position. Thiscorresponds to the progressive establishment of the maximum operativepressure in the delivery circuit 13 and in the chamber 4 of jack 1.

The shank 61 follows the displacement towards the left of the secondslide valve 64. The cam 63 then moves away from the switch FC permittingthe switch to reclose and then the cam 62 operates the switch PCindicating that the slide valve 64 occupies its closed position, i.e.which indicates that the maximum operative pressure has beenestablished.

The piston 2 of jack 1 moves in its reverse direction under the effectof this pressure. The cam 80 moves away from the switch FC permittingthe latter to open, thereby removing the energization from relay R Thecontact R re-closes, but the relay R cannot be energized since theswitch Dc and the contact R are open. Simultaneousely with thede-energization of the relay R the contact R opens. However, theexcitation of relay R is maintained through the intermediary of theclosed contaCtS R21, R51 and C22.

(f) Automatic stopping of the return cycle, i.e. of the complete workcycle of piston 2 This operation corresponds to the progressive removalof the pressure in the delivery circuit 13 and in the chamber 4 of jack1.

At the end of the return travel of piston 2 the cam 80 closes the switchFC thereby permitting the energization of the relay R causing theopening of contact R The relay R becomes de-energized with the resultthat its contacts R R R and R open.

The relay C remains energized through the intermediary of the closedswitches F and FC while the relay C remains energized through theintermediary of the closed contacts R and C On the other hand, the relayC becomes de-energized since the contact R opens and the contact R waspreviously opened (prior to the reversal of the principal slide valve12).

The contact C opens and the electro-magnet EA; is de-energized, thuspermitting the spring 72 to urge the second master slide valve 64 intoits neutral position.

As a result, the cam 62 moves away from the switch PC and then the cam63 opens the switch FC so that the latter switch disconnects theenergizing current from the relay C The contact C opens and theelectro-magnet EA is de-energized, permitting the spring 48 to urge thefirst master slide valve 56 into its neutral position. The shank 51 alsomoves towards the right under the influence of said spring 48. The cam52 moves away from switch FC permitting the switch to open, and the cam53 closes the switch FC thereby permitting the re-energization of relayR At this moment, the contacts R and R open and the contacts R and Rclose. The opening of contact R results in a de-energization of relay CThe contact C opens and the electro-magnet EA is de-energized, whichpermits spring 36 to urge the principal slide valve 12 into its neutralposition. In following this movement, the cam 43 moves away from theswitch FC permitting the latter to open.

The stopping of the entire apparatus is etfectuated by the momentarydepression of switch Am.

The hydraulic anti-shock device having two master slide valves couldalso be controlled in a semi-automatic fashion. To this end, one may usethe electric circuit shown in FIG. 3, completed by the group G of FIG. 5and in which the group G of FIG. 3 is replaced by the group G of FIG. 5.The operation of this embodiment is the same as that described inparagraphs III and V, above.

Of course, the various embodiments have only been given by way ofexample, and numerous modifications can be made thereto withoutdeparting from the spirit of this invention. For example, the masterslide valves could also be of simple stop-valve type. In place of themaster distributors utilizing slide valves, one could also provideelectro-magnetic valves of any known type. The operation of the deviceof the present invention could deviate from that which has beendescribedabove. Thus, it would be possible to manually actuate thevarious distributors. After the energization of the advance-controlrelay R it is also possible to anticipate the operation of the masterdistributors by manually actuating them in the direction which theywould be given by the excitation of their corresponding electro-magnets.Similarly, because of the addition of a mass to the control shank of thedistributors, the successive energizations of the electro-magnets of themaster distributors could be delayed. It should also be noted that thearrangement of the present device permits the advance and return of thejack-piston to be stopped at any desired moment, at any position in itstravel path, and this could be carried out in an extremely rapid fashionand without the formation of any shock waves or vibrations. The factthat the sequence of operations is constantly monitored by theend-of-travel switches, and in such a manner that the followingoperation can only be carried out after the accomplishment of thepreceding operation, and the fact that this monitoring is linked to thepositions of the distributors, gives to this hydraulic anti-shock devicea high degree of effectiveness, security, and rapidity of operation. Thehydraulic antishock device could also be applied to the control of ajack comprising a single acting piston. It should also be noted that theapplication of the present invention is not limited to a jack in whichthe piston moves in an alternating linear path, but it may also be usedfor pistons having non-linear alternating or continuous movements and torotating hydraulic motors.

The present invention has been described in connection with embodimentswhich consist in the utilization of distributors referred to as havingopen centres; but it would be possible, according to operatingrequirements, to utilize distributors having closed ends, or semi-closedends, i.e. in so far as concerns the principal distributor, the deliverycircuit and the vat-return circuit, as well as the two jack-feedingcircuits, could be blocked.

I claim:

1. A hydraulic anti-shock device associated with a hydraulic jackfurnished with a piston the two faces of which, through the intermediaryof a principal distributor controlled alternately by twoelectro-magnets, are adapted to be connected either alternately with thedelivery circuit of a pump or the pump inlet by its return circuit, orsimultaneously with said two circuits, and comprising: in the deliverycircuit downstream of the principal regulator, a pressure regulatorfurnished with a closing valve interposed between the delivery circuitand the return circuit, and rigidly connected to a piston defining twochambers the lower chamber of which communicates directly with thedelivery circuit and the upper chamber of which, furnished with arestraining spring urging the valve into its closing position,communicates through the intermediary of a calibrated channel with thedelivery circuit; a master distributor connected, on the one hand, tothe upper chamber of the valve piston and, on the other hand, to thereturn circuit, and adapted to be controlled by an electro-magnet insuch a manner as to destroy or establish the communication between theupper chamber of said valve piston and the return circuit; and anelectric circuit furnished with switches and relays for starting andstopping a motor driving the pump and for controlling the variouselectro-magnets, said device being characterized in that it comprises:end or travel switches adapted to be actuated by cams arranged in such amanner as to be able to follow the displacements of the armatures of thecorresponding electromagnets of the distributors, the end of travelswitch for the master distributor being disposed in the electric circuitof the electromagnets of the principal distributor in such a way thatthey can only be closed by their corresponding cams and can only. permitthe energization of the electromagnets of the principal distributor whenthe master distributor is in its neutral position, while the end oftravel switches of the principal distributor are disposed in the circuitof the electromagnet of the master distributor in such a way thatneither can be closed by its corresponding cam and does not permit theenergization of the electromagnet of the master distributor until theprincipal distributor occupies one of its two extreme positions.

2. A device according to claim 1 wherein the cams of the end of travelswitches of the principal distributors are mounted on a control shankcooperating with the corresponding slide valve of the distributorthrough the intermediary of the electromagnets.

3. A device according to claim 1 characterized in that the cam of theend of travel switch of the master slide valve is mounted on a controlshank cooperating with the corresponding slide valve of the masterdistributor through the intermediary of its electromagnet.

4. A device according to claim 1, characterized in that a shankcooperating with the electro-magnet of the master distributor isfurnished with two cams each of which cooperates with a correspondingend of travel switch, these two cams being mounted on said shank in sucha way that, when one of the cams closes its corresponding switch, theother cam permits the opening of the other switch, one of the switchesbeing closed when the master slide valve occupies its neutral positionand being interposed in the electric control and monitoring circuit andadapted to monitor the energization and the deenergization of one or theother of the electro-magnets of the principal distributor, while theother switch is closed when the master slide valve occupies its closingposition and is interposed in the electric supply line for a device forproducing a visible or audible signal.

5. A device according to claim 1, characterized in that, at one of theirends, the control shanks associated with the principal and masterdistributors are furnished with weak springs adapted to urge theirrespective shanks against the armature of the electro-magnet of thecorresponding distributor.

6. A device according to claim 1, characterized in that, at one of itsends, each of the control shanks associated with the principal andmaster distributors is furnished with a push-button which permits themanual actuation of the slide valve of the corresponding distributor.

7. A device according to claim- 6 characterized in that each push buttonis constituted by a certain inertia mass adapted to slow down thedisplacements of each respective control shank with respect to the speedof displacement of the corresponding distributor slide valve andelectro-magnet armature.

8. A device according to claim 1 characterized in that the electriccontrol and monitoring circuit is connected to a source of alternatingcurrent and comprises several groups of electrical elements, whichgroups are mounted in parallel with one another and include, a firstgroup adapted to control the starting and stopping of the pump motor andto simultaneously control the supply of current to the other groups; asecond group adapted to control the energization and deenergization, onthe one hand, of one of the electromagnets of the principal distributorand, on the other hand, of the electro-magnet of the master distributor;a third group adapted to control the first electro-magnet of theprincipal distributor in such a manner that, when it is energized, thiselectromagnet urges the slide valve of the principal distributor into aposition corresponding to the advance of the jack piston; a fourth groupadapted to control the electromagnet of the master distributor in such away that,

in its energized state, this electromagnet urges the master distributorslide valve into a position which produces a progressive increase in thepressure of the fluid in the delivery circuit; a fifth group, adapted tocontrol the second electromagnet of the principal distributor in such aman her that, in its energized state, this electromagnet urges the slidevalve of the principal distributor into a position corresponding to thereturn of the jack piston; and a sixth group adapted to monitor thesupply of current to the third and fifth groups.

9. A device according to claim 8, characterized in that each group ofelectrical elements comprises at least one relay.

10. A device according to claim 8, characterized in that the first groupof electric elements comprises: a relay for controlling the motor; afirst manual switch, which is normally open, for starting the device,and a second manual switch, which is normally closed, for stopping thedevice; these switches being mounted in series with one another and withsaid relay, said relay comprising: a first holding contact connected inparallel across the terminals of the first-recited switch; a secondcontact mounted in series with the line feeding the other groups; and agroup of three contacts interposed in the line feeding the pump motor,these five contacts being closed when their relay is energized.

11. A device according to claim 8 characterized in that the second groupof electric elements comprises: two monitoring relays, one of whichmonitors the advance of the jack piston and the other of which monitorsthe return of the jack piston, the two relays being mounted in parallel,a first manual switch for starting the advance cycle of the jack andmounted in parallel with a holding contact of the advance monitoringrelay, these contacts and said first switch each being mounted in serieswith said advance monitoring relay; a second manual switch for startingthe return cycle of the jack and mounted in parallel with a holdingcontact of the return monitoring relay, this contact and the secondswitch each being mounted in series with the return monitoring relay;and a third manual switch for stopping the cycle of operations, thisswitch being normally closed and being mounted in series with theholding contacts and with said cycle starting switches, the latter beingnormally open, said holding contacts being closed when theircorresponding relay is energized.

12. A device according to claim 8 characterized in that the third groupof electrical elements comprises: an advance control relay; the windingof the first electromagnet of the principal slide valve; and a firstcontact which is normally open and which is controlled by said relay,this contact and this winding being mounted in series with one anotherand in parallel with said relay; a second normally closed contactmounted in series with said relay and controlled by a relay of the fifthgroup of elements; a third normally closed contact mounted in serieswith the second contact and controlled by a relay of the sixth group ofelements; a fourth normally open contact mounted in parallel with thethird contact and controlled by the advanced monitoring relay; a fifthnormally opened contact mounted in series with the fourth contact and inparallel with the third contact, and controlled by the relay of thesixth group; and a sixth holding contact, which is normally opened,mounted in parallel with the fifth contact and controlled by theadvanced control relay.

13. A device according to claim 8 characterized in that the fourth groupof electric elements comprises: a relay for controlling the masterdistributor; the winding of the electro-magnet of the master slide valveand a first normally opened contact, this winding and this contact beingmounted in series with one another and in parallel with said relay;second and third normally opened contacts mounted in parallel with oneanother and in series with said relay, the second contact beingcontrolled by the advanced monitoring relay and the third contact beingcontrolled by the return monitoring relay; and the two end of travelswitches of the principal distributor, which switches cooperate with thetwo cams mounted on the shank of the principal slide valve, theseswitches being mounted in parallel With one another and in series withthe second and third contacts and being normally opened when they arenot actuated by their corresponding cams.

14. A device according to claim 8 characterized in that the fifth groupof electric elements comprises: a return control relay; the Winding ofthe second electro-magnet of the principal slide valve and a firstnormally open contact controlled by said relay, this winding and thiscontact being mounted in series with one another and in parallel withsaid relay; a second normally closed contact mounted in series with saidrelay and controlled by the advanced control relay; a third normallyclosed contact mounted in series with the second contact and controlledby the relay of the sixth group; a fourth normally open contact mountedin parallel with the third contact and controlled by the returnmonitoring relay; a fifth normally open contact mounted in series withthe fourth contact and in parallel with the third contact and controlledby the relay of the sixth group; and a sixth normally opened holdingcontact mounted in parallel with the fifth contact and controlled by thereturn control relay.

15. A device according to claim 8 characterized in that the sixth groupof electrical elements comprises: a minimum operative pressuremonitoringrelay mounted in series with that one of the end of travel switches ofthe master distributor which is closed when the master slide valve is inits neutral position.

16. A device according to claim 1, characterized in that it comprises asecond master distributor having a slide valve which is also furnishedwith an electromagnet adapted to act against the force of a restrainingspring of said slide valve; this second master distributor beingconnected, on the one hand, to the conduit between the principalpressure regulator and the first master distributor and, on the otherhand, to the inlet vat return circuit through the intermediary of anauxiliary pressure regulator; the slide valve of said second masterdistributor being adapted to displace a shank furnished with two camseach of which is adapted to cooperate with an end of travel switch, oneof these end of travel switches being adapted to interrupt theenergization current of the electromagnet of the first masterdistributor when the slide valve of the second master distributorestablishes a hydraulic communication between the principal pressureregulator and the auxiliary regulator, while the other end of travelswitch is mounted to control a unit producing and audible or visualsignal when said slide valve interrupts the hydraulic communicationbetween the principal pressure regulator and the auxiliary pressureregulator.

17. A device according to claim 1, characterized in that the shank ofthe jack piston is furnished with a cam adapted to cooperate alternatelywith an end of advance travel switch and an end of return travel switchwhen said piston is in a respective one of its extreme positions, insuch a way that the end of advance travel switch, through theintermediary of the electric circuit, controls the denergization of theelectromagnet of the master distributor, then the deenergization of thefirst electro-magnet, then the energization of the secondelectro-magnet, of the principal distributor, and then the reexcitationof the electro-magnet f the master distributor, and also in such a waythat the end of return travel switch, also through the intermediary ofthe electric circuit, controls the deenergization of the electro-magnetof the master distributor, and then the denergization of the secondelectromagnet of the principal distributor.

18. A device according to claim 1 characterized in that, when the shankof the jack piston is adapted to selectively actuate, through theintermediary of a cam, two end of travel switches, the electric controland monitoring circuit further comprises a seventh and an eighth groupmounted in parallel with the other groups of the elements; the seventhgroup comprising an end of advance travel and reversal monitoring relaymounted in series with the end of advance travel switch, which switch isnormally open when it is not actuated by said cam; the eighth groupcomprising an end of return travel monitoring relay mounted in serieswith the end of return travel switch, which switch is normally open whenit is not actuated by said cam; and the second group of electricalelement comprising, on the one hand, a normally closed contactcontrolled by the end of travel relay and mounted in series with theadvanced monitoring relay and, on the other hand, in place of the returncycle manual starting switch, four contacts mounted in series with thereturn monitoring relay; said four contacts comprising: a first normallyclosed contact controlled by the advance control relay; a secondnormally closed contact controlled by the end of return travelmonitoring relay; a third normally closed contact controlled by theadvanced monitoring relay; and a fourth normally opened contactcontrolled by the end of advance travel monitoring relay, the last twoof said contacts being mounted in parallel and the first two of saidcontacts being mounted in series with the holding contact of the returntravel monitoring relay.

19. A device according to claim 1, characterized in that the group ofelectric elements comprising the relay for the first master distributorincludes one of the end of travel switches of the second masterdistributor, this switch being mounted in parallel with the two parallelconnected contacts and being controlled, respectively, by the advancedmonitoring relay and the return monitoring relay, and being opened whenit is actuated by its corresponding cam.

26. A device according to claim 16, characterized in that it furthercomprises a group of electrical elements controlling the displacementsof the slide valve of the second master distributor, this groupcomprising: a second master distributor control relay; the winding ofthe electromagnet of the second master distributor; a normally opencontact controlled by said relay, this winding and this contact beingmounted in series with one another and in parallel with said relay; oneof the end of travel switches of the first master distributor, thisswitch being mounted in series with said relay and being closed when thefirst master distributor assures the communication between the principalpressure regulator and the inlet vat return circuit, and two normallyopen contacts, mounted in parallel with one another and in series Withsaid relay through the intermediary of said switch, one of these twocontacts being adapted to be controlled by the advanced monitoring relaywhile the other of these contacts is adapted to be controlled by thereturn monitoring relay.

References Cited by the Examiner UNITED STATES PATENTS 2,267,177 12/1941 Twyman 60-52 2,277,640 3 1942 Harrington 6052 2,287,559 6/1942 Nye.

2,318,851 5/1943 Griflith 60-97 X EDGAR W. GEOGHEGAN, Primary Examiner.

1. A HYDRAULIC ANTI-SHOCK DEVICE ASSOCIATED WITH A HYDRAULIC JACKFURNISHED WITH A PISTON THE TWO FACES OF WHICH, THROUGH THE INTERMEDIARYOF A PRINCIPAL DISTRIBUTOR CONTROLLED ALTERNATELY BY TWOELECTRO-MAGNETS, ARE ADAPTED TO BE CONNECTED EITHER ALTERNATELY WITH THEDELIVERY CIRCUIT OF A PUMP OR THE PUMP INLET BY ITS RETURN CIRCUIT, ORSIMULTANEOUSLY WIITH SAID TWO CIRCUITS, AND COMPRISING: IN THE DELIVERYCIRCUIT DOWNSTREAM OF THE PRINCIPAL REGULATOR, A PRESSURE REGULATORFURNISHED WITH A CLOSING VALVE INTERPOSED BETWEEN THE DELIVERY CIRCUITAND THE RETURN CIRCUIT, AND RIGIDLY CONNECTED TO A PISTON DEFINING TWOCHAMBERS THE LOWER CHAMBER OF WHICH COMMUNICATES DIRECTLY WITH THEDELIVERY CIRCUIT AND THE UPPER CHAMBER OF WHICH, FURNISHED WITH ARESTRAINING SPRING URGING THE VALVE INTO ITS CLOSING POSITION,COMMUNICATES THROUGH THE INTERMEDIARY OF A CALIBRATED CHANNEL WITH THEDELIVERY CIRCUIT; A MASTER DISTRIBUTOR CONNECTED, ON THE ONE HAND, TOTHE UPPER CHAMBER OF THE VALVE PISTON AND, ON THE OTHER HAND, TO THERETURN CIRCUIT, AND ADAPTED TO BE CONTROLLED BY AN ELECTRO-MAGNET INSUCH A MANNER AS TO DESTROY OR ESTABLISH THE COMMUNICATION BETWEEN THEUPPER CHAMBER OF SAID VALVE PISTON AND THE RETURN CIRCUIT; AND ANELECTRIC CIRCUIT FURNISHED WITH SWITCHES AND RELAYS FOR STARTING ANDSTOPPING A MOTOR DRIVING THE